Electroerosion machining systems and methods

ABSTRACT

An electroerosion machining system comprises one or more electrodes configured to machine a workpiece, a power supply configured to energize the workpiece and the respective one or more electrodes, an electrolyte supply configured to pass an electrolyte, and a working apparatus configured to move the respective one or more electrodes relative to the workpiece. The electroerosion machining system further comprises a controller configured to control the working apparatus to machine the workpiece, and a removal agent configured to cooperate with the electrolyte from the electrolyte supply for removal of removed material from the workpiece. An electroerosion machining method is also presented.

BACKGROUND

This invention relates generally to electroerosion machining systems andmethods. More particularly, this invention relates to electroerosionmachining systems and methods with higher flushing capabilities formachining workpieces.

Electrochemical machining (ECM) and electrical discharge machining (EDM)are conventional processes for machining material in objects such as gasturbine components. ECM processes typically pass an electrical currentin the gap between an electrode(s) and a workpiece for precision removalof amounts of material on the workpiece to achieve a desired finalconfiguration thereof with substantially smooth surfaces. EDM processescirculate a dielectric liquid between an electrode(s) and a workpiece,and electrical discharges are generated in the gap between the electrodeand the workpiece.

Both ECM and EDM processes use electrical current under direct-current(DC) voltage to electrically power removal of the material from theworkpiece. However, in ECM, an electrolyte (an electrically conductiveliquid) is circulated between the electrode(s) and the workpiece forpermitting electrochemical dissolution of the workpiece material, aswell as cooling and flushing the gap region therebetween. In contrast,EDM processes circulate a nonconductive (dielectric) liquid in the gapto permit electrical discharges in the gap to remove the workpiecematerial. As used herein, the term “electroerosion” should be understoodto apply to those electromachining processes that circulate anelectrolyte (electrically conductive liquid) in the gap between theelectrode(s) and the workpiece, these processes enabling a high rate ofmaterial removal and reducing thermal damages to the workpiece.

Electroerosion machining is generally a thermal based material removalprocess. During machining, removed material (chips) from the workpiecemay be typically in a molten/liquid phase and it is important to ejectthe molten chips effectively from cutting zones. However, in someapplications, during conventional electroerosion machining, due toinsufficient flushing capabilities, the molten chips may interact withthe workpiece being machined so as to stick or attach to the workpieceand transfer excess thermal energy into the workpiece resulting in heataffected zone on the workpiece and undesirable material properties. Thismay be disadvantageous for subsequent electroerosion machining and themachining quality of the workpiece.

Therefore, there is a need for new and improved electroerosion machiningsystems and methods with higher flushing capabilities for machiningworkpieces.

BRIEF DESCRIPTION

An electroerosion machining system is provided in accordance with oneembodiment of the invention. The electroerosion machining systemcomprises one or more electrodes configured to machine a workpiece, apower supply configured to energize the workpiece and the respective oneor more electrodes, an electrolyte supply configured to pass anelectrolyte between the workpiece and the respective one or moreelectrodes, and a working apparatus configured to move the respectiveone or more electrodes relative to the workpiece. The electroerosionmachining system further comprises a controller configured to controlthe working apparatus to machine the workpiece, and a removal agentconfigured to cooperate with the electrolyte from the electrolyte supplyfor removal of removed material from the workpiece.

An electroerosion machining method is provided in accordance withanother embodiment of the invention. The electroerosion machining methodcomprises driving one or more electrodes to move relative to aworkpiece, passing an electric current between the respective one ormore electrodes and the workpiece while passing an electrolyte from anelectrolyte supply through a gap defined therebetween, and introducing aremoval agent between the respective one or more electrodes and theworkpiece to cooperate with the electrolyte for removal of removedmaterial from the workpiece out of the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic diagram of an electroerosion machining system inaccordance with one embodiment of the invention;

FIGS. 2-3 are schematic diagrams showing surface comparison of aworkpiece machined with and without a removal agent; and

FIGS. 4-5 are schematic diagrams of the electroerosion machining systemin accordance with another two embodiments of the invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

Preferred embodiments of the present disclosure will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the disclosure in unnecessarydetail.

FIG. 1 illustrates a schematic diagram of an electroerosion machiningsystem 10 in accordance with one embodiment of the invention. Inembodiment of the invention, the electroerosion machining system 10 isused to remove material from a workpiece 100, such as titanium alloylayer by layer to form a desired configuration. As illustrated in FIG.1, the electroerosion machining system 1 comprises a numerical control(NC) or computer numerical control (CNC) device (not shown) including aworking apparatus 11 and a controller 12, a power supply 13, anelectrolyte supply 14, and an electrode 15. In one non-limiting example,the electroerosion machining system 1 comprises a high speedelectroerosion (HSEE) machining system.

In embodiments of the invention, the NC or the CNC device can be used toperform traditional automated machining. In particular examples, theworking apparatus 11 may comprise a machine tool or lathe includingservomotors (not shown) and spindle motors (not shown). The electrode 15is mounted on the working apparatus 11 for performing electroerosionmachining. Accordingly, the servomotors may drive the electrode 15 andthe workpiece 100 to move relative to each other at a desired speed andpath, and the spindle motors drive the electrode 15 to rotate at adesired speed.

The controller 12 comprises pre-programmed instructions based ondescriptions of the workpiece 100 in a computer-aided design (CAD)and/or a computer-aided manufacturing (CAM), and is connected to theworking apparatus 11 to control the working apparatus 11 to drive theelectrode 15 to move and/or rotate according to certain operationalparameters, such as certain feedrates, axes positions, or spindle speedsetc. Additionally, the controller 12 is also connected to the powersupply 13 to monitor the status of voltages and/or currents in a gap 16between the electrode 15 and the workpiece 100 so as to control themovement of the working apparatus 11 holding the electrode 15.

In non-limiting examples, the controller 12 may be a general controllerand comprise central processing units (CPU), read only memories (ROM),and/or random access memories (RAM), as known to one skilled in the art.In one non-limiting example, the controller 12 comprises a controller,sold under the tradename GE-FANUC 18i CNC, by GE-Fanuc, ofCharlottesville, Va.

In the illustrated embodiment, the power supply 13 comprises a directcurrent (DC) pulse generator. The electrode 15 and the workpiece 100 areconnected to negative and positive poles of the power supply 13,respectively. Accordingly, in embodiments of the invention, theelectrode 15 may function as a cathode and the workpiece 100 may act asan anode. In other embodiments, the polarities on the electrode 15 andthe workpiece 100 may be reversed. In certain applications, the powersupply 13 may not be connected to the controller 12.

In one example, the electrolyte supply 14 may be in communication withand receive the pre-programmed instructions from the controller 12 forpassing an electrolyte between the electrode 15 and the workpiece 100.Alternatively, the electrolyte supply 14 may be disposed separately. Inthe illustrated embodiment, a nozzle 17 is employed to be in fluidcommunication with the electrolyte supply 14 for projecting theelectrolyte to pass between the electrode 15 and the workpiece 100. Inother examples, more than one nozzle may be employed for projection ofthe electrolyte from the electrolyte supply 14.

Thus, during electroerosion machining, the power supply 13 may pass apulse electric current between the electrode 15 and the workpiece 100 toremove material from the workpiece 100 layer by layer for forming adesired configuration while the electrolyte passes between the electrode15 and the workpiece 100 to carry the removed material (chips) 101 outof the gap 16. In the illustrated embodiment, the electrode 15 comprisesa wheel shape. An arrow 18 indicates a flow direction of theelectrolyte. In some applications, the electrode 15 may have othershapes, such as rectangular shapes or shapes having tubularcross-sections.

In certain applications, during electroerosion machining, the removedmaterial may not be carried out of the gap 16 effectively. As a result,at least a portion of the removed material may stick to a surface of theworkpiece to be machined and transfer excess thermal energy into theworkpiece resulting in heat affected zone (HAZ) on the workpiece andundesirable material properties. For example, during electroerosionmachining of Ti-alloy, when Ti-alloy is heated and rapidly quenched bythe electrolyte, alpha/beta Ti in Ti-alloy may have a phase transitionto change into brittle alpha, which is disadvantageous to effectivenessof such a thermal based material removal process.

Accordingly, in order to avoid and/or alleviate generation ofundesirable material properties and the heat affected zone on theworkpiece, in some embodiments, as illustrated in FIG. 1, theelectroerosion machining system 10 may further comprise a removal agent19 to cooperate with the electrolyte supply 14 for facilitating removalof the removed material out of the gap 16. In non-limiting examples, aremoval agent supply 102 may be employed to supply the removal agent 19.

In some examples, the removal agent 19 may comprise one or more ofcopper powder, non-conducting materials, nitrogen containinghydrocarbons, and other suitable materials. In non-limiting examples,the non-conducting materials may comprise aluminum oxide, carbides,nitrides, resins, diamond, and garnet. The nitrogen containinghydrocarbons may comprise amines. The carbides may comprise siliconcarbide, tungsten carbide and boron carbide. The nitrides may comprisecubic boron nitride (CBN). The resins may comprise phenolic andpolyimide. In some application, the removal agent 19 may be in a form ofparticles, and the size distribution of the particles may be determinedbased on different applications.

In the illustrated embodiment, the removal agent 19 is in fluidcommunication with the nozzle 17 of the electrolyte supply 14. Thus,during electroerosion machining, the removal agent 19 may be mixed anddispersed into the electrolyte for passing between the electrode 15 andthe workpiece 100 to facilitate removal of the removed material out ofthe gap 16. In some non-limiting examples, the removal agent 19 mayfunction as additives to be dispersed in the electrolyte in a form ofseparated solid particles.

In certain applications, the removal agent 19 may comprise more than oneof the copper powder, non-conducting materials, nitrogen containinghydrocarbons, carbides, nitrides, resins, diamond, and other suitablematerials. In one non-limiting example, the removal agent 19 maycomprise a mixture of the non-conducting materials, such as aluminumoxide and the nitrogen containing hydrocarbons, such as amines. In thisexample, during electroerosion machining, with the introduction of theremoval agent 19 between the electrode and the workpiece, the dischargefrom the power supply 13 may change into transient electric arc betweenthe electrode 15 and the workpiece 100 due to the presence of thenon-conducting materials, such as aluminum oxide, so that the thermalimpact to the workpiece may be alleviated and lower electrical energymay also be consumed.

Further, during ejection of the removal agent 19 and the electrolytefrom the nozzle 17, aluminum oxide cooperates with the electrolyte togenerate relatively higher momentum to remove the removed material fromthe surface of the workpiece 100 to be machined. Meanwhile, the nitrogencontaining hydrocarbons, such as amines may also change chemicalcomposition of the molten chips 101 in molten zones/cutting zones (notlabeled) so that the surface tension of the molten chips may be changedaccordingly so as to reduce affinity of the molten chips on theworkpiece. As a result, with the cooperation of the removal agent 19 andthe electrolyte during the electroerosion machining, the molten chipsmay be removed effectively out of the gap 16 and the heat affected zoneson the workpiece 100 may be avoided and/or alleviated.

Table-1 illustrates comparison of results of three exemplary experimentsfor machining the workpiece, such as Ti-alloy. Experimental conditionsin each of the three exemplary experiments comprise a voltage of about15 volts between the electrode and the workpiece, and a depth of cut(DOC) of about 0.02 inch each cut. As can be seen, in the firstexemplary experiment without employment of the removal agent 19, theheat affected zone is about 674 um and the consumed electrical energy isabout 30700J. In the second exemplary experiment with employment ofphenolic, the heat affected zone is about 383 um and the consumedelectrical energy is about 6150J. In the third exemplary experiment withemployment of polyimide, the heat affected zone is about 238 um and theconsumed electrical energy is about 5810J.

TABLE 1 Voltage HAZ Removal agent DOC Consumed energy 15 v 647 um — 0.02inch 30700 J  15 v 383 um phenolic 0.02 inch 6150 J 15 v 238 umpolyimide 0.02 inch 5810 J

As illustrated in Table-1, compared with the exemplary experimentwithout employment of the removal agent 19, in the exemplary experimentswith employment of the removal agent 19, the heat affected zones and theconsumed energy are both smaller, so that machining efficiency andquality may be enhanced.

FIGS. 2-3 illustrate schematic diagrams showing surface comparison of aworkpiece, such as Ti-alloy machined with and without the removal agent19, respectively. In the experiment shown in FIG. 2, the removal agent19 comprises garnet. As compared, the machined surface of the workpiece100 in the experiment with the garnet is smooth and has less thermalimpact than the machined surface of the workpiece 100 in the experimentwithout the garnet, as shown in FIG. 3.

FIG. 4 illustrates a schematic diagram of the electroerosion machiningsystem 10 in accordance with another embodiment of the invention. Foreasy illustration, the removal agent 19, the electrolyte (not labeled),the electrode 15 and the workpiece 100 are illustrated and otherelements are not illustrated. As illustrated in FIG. 4, the electrode 15has the wheel shape. The removal agent 19 comprises a plurality ofabrasive elements 20 disposed separately around and integrated with theelectrode. In non-limiting examples, the abrasive elements may besintered together with the electrode 15. In some applications, theabrasive elements 20 of the removal agent 19 may be nonconductive andhave desired hardness. In non-limiting examples, the abrasive elements20 may comprise nonconductive materials, such as aluminum oxide andtungsten carbide.

For the illustrated arrangement, the abrasive elements 20 may protrudebeyond an outer surface 21 of the electrode 15 and be spaced away fromeach other. The electrode 15 may be segmented into a plurality of spaceddischarge sections (not labeled) by the abrasive elements 20. Thedischarge sections and the abrasive elements 20 may be disposedalternately for performing the electroerosion machining.

As depicted in FIG. 4, during electroerosion machining, the power supply13 passes the pulse electric current between the electrode 15 and theworkpiece 100. The discharge sections of the electrode 15 and theabrasive elements 20 may be disposed alternately, so that afterdischarge of the discharge zones, the discharge may be paused and theadjacent abrasive elements 20 are introduced to pass the respectivecutting zones for removal of the molten chips 101 in cooperation withthe electrolyte.

Accordingly, with the electrolyte passing between the electrode 15 andthe workpiece 100 to carry the molten chips 101 out of the gap 16, theprotruding abrasive elements 20 may wipe alternately to detach theremoved material from the workpiece to facilitate removal of the removedmaterial out of the gap 16 to alleviate the thermal impact on theworkpiece 100. In certain applications, during machining, the abrasiveelements 20 may be attrited.

In certain applications, in order to alleviate the thermal impact on theworkpiece, more than one electrode may also be employed and be locatedseparately and alternately. Thus, similar to the arrangement in FIG. 4,the discharge or the electrodes may also be performed alternately toalleviate thermal impact on the workpiece.

FIG. 5 illustrates a schematic diagram of the electroerosion machiningsystem 10 employing a plurality of electrodes 16. Similar to thearrangement in FIG. 4, for easy illustration, some elements are notillustrated in FIG. 5. As illustrated in FIG. 5, the electroerosionmachining ID comprises a base 22 for holding the electrodes 16 and beingassembled onto the working apparatus 11. For the illustratedarrangement, the base 22 comprises a wheel shape and defines a pluralityof slots 23 and a plurality of channels 24 in fluid communication withthe slots 23 and a central hole 25.

In some examples, the slots 23 may be defined separately along acircumference of the base 22 for accommodation of the respectiveelectrodes 16. The channels 24 may be used for the electrolyte passingthrough. The central hole 25 may be in fluid communication with theelectrolyte supply 14. During electroerosion machining, with therotation of the base 20, the discharge between the workpiece 100 and therespective electrodes 16 may also be performed alternately so as toalleviate the thermal impact on the workpiece 100 while the electrolytepasses between the base 22 and the workpiece 100 to remove the moltenchips.

It should be noted that the arrangements in FIGS. 1-5 are merelyillustrative. In some applications, for the arrangement in FIG. 5,during machining, similar to the arrangement in FIG. 1, the removalagent 19 may also be mixed into the electrolyte for facilitation ofremoval of the removed material. Although the electrodes 16 compriserectangular shapes, the electrodes 16 may have other shapes, such ascircular or wheel shapes. In certain applications, the abrasive elementsshown in FIG. 4 may also be employed for the arrangement in FIG. 5.

In embodiments of the invention, due to employment of the removal agentduring electroerosion machining, the molten chips may be removed fromcutting zone and out of the gap effectively. This may avoid and/oralleviate thermal impact on the workpiece so as to improve the machiningquality. In some applications, the removal agent may be dispersed intothe electrolyte so as to retrofit conventional electroerosion machiningsystems and increase system flexibility.

In other applications, the removal agent may be integrated with theelectrode alternately and/or a plurality of separated electrodes may beemployed to enhance removal of the molten chips out of the gap andalleviate thermal impact on the workpiece via alternating discharge. Incertain application, the power supply may comprise the direct current(DC) pulse generator, which also may alleviate thermal impact on theworkpiece via the alternating discharge. In particular examples, duringthe electroerosion machining of Ti-alloy, for the arrangements of theinvention, the phase transition of Ti may be avoided and/or reduced, andthe machining quality may be higher.

While the disclosure has been illustrated and described in typicalembodiments, it is not intended to be limited to the details shown,since various modifications and substitutions can be made withoutdeparting in any way from the spirit of the present disclosure. As such,further modifications and equivalents of the disclosure herein disclosedmay occur to persons skilled in the art using no more than routineexperimentation, and all such modifications and equivalents are believedto be within the spirit and scope of the disclosure as defined by thefollowing claims.

1. An electroerosion machining system, comprising: one or moreelectrodes configured to machine a workpiece; a power supply configuredto energize the workpiece and the respective one or more electrodes; anelectrolyte supply configured to pass an electrolyte between theworkpiece and the respective one or more electrodes; a working apparatusconfigured to move the respective one or more electrodes relative to theworkpiece; a controller configured to control the working apparatus tomachine the workpiece; and a removal agent configured to cooperate withthe electrolyte from the electrolyte supply for removal of removedmaterial from the workpiece.
 2. The electroerosion machining system ofclaim 1, wherein the removal agent comprises one or more of aluminumoxide, carbides, nitrides, resins, diamond, garnet and nitrogencontaining hydrocarbons.
 3. The electroerosion machining system of claim2, wherein the carbides comprise one or more of silicon carbide,tungsten carbide and boron carbide, the nitrides comprise cubic boronnitride, the resins comprise one or more of phenolic and polyimide; andthe nitrogen containing hydrocarbons comprise amines.
 4. Theelectroerosion machining system of claim 1, wherein the removal agent isdispersed into the electrolyte to pass between the workpiece and therespective one or more electrodes.
 5. The electroerosion machiningsystem of claim 4, further comprising a removal agent supply configuredto provide the removal agent, and wherein the removal agent is in a formof solid particles.
 6. The electroerosion machining system of claim 4,further comprising a nozzle configured to eject a mixture of theelectrolyte and the removal agent to pass between the respective one ormore electrodes and the workpiece.
 7. The electroerosion machiningsystem of claim 1, wherein the removal agent is disposed on therespective one or more electrodes.
 8. The electroerosion machiningsystem of claim 7, wherein the removal agent comprises a plurality ofabrasive elements, and wherein the abrasive elements disposed on thesame one electrode are disposed alternately around and protrude beyondthe one electrode.
 9. The electroerosion machining system of claim 1,further comprising a base assembled onto the working apparatus andconfigured to hold the one or more electrodes, and wherein more than oneof the one or more electrodes are disposed on the base alternately. 10.The electroerosion machining system of claim 9, wherein the base definesa plurality of slots to hold the respective more than one electrode, acentral hole in fluid communication with the electrolyte supply and aplurality of channels in fluid communication with the central hole andthe respective slots.
 11. The electroerosion machining system of claim9, where the base has a wheel shape.
 12. The electroerosion machiningsystem of claim 1, wherein the one or more electrodes comprise wheelshapes.
 13. An electroerosion machining method, comprising: driving oneor more electrodes to move relative to a workpiece; passing an electriccurrent between the respective one or more electrodes and the workpiecewhile passing an electrolyte from an electrolyte supply through a gapdefined therebetween; and introducing a removal agent between therespective one or more electrodes and the workpiece to cooperate withthe electrolyte for removal of removed material from the workpiece outof the gap.
 14. The electroerosion machining method of claim 13, whereinthe removal agent comprises one or more of aluminum oxide, carbides,nitrides, resins, diamond, garnet and nitrogen containing hydrocarbons.15. The electroerosion machining method of claim 14, wherein thecarbides comprise one or more of silicon carbide, tungsten carbide andboron carbide, the nitrides comprise cubic boron nitride, the resinscomprise one or more of phenolic and polyimide, and the nitrogencontaining hydrocarbons comprise amines.
 16. The electroerosionmachining method of claim 13, wherein the removal agent is mixed anddispersed into the electrolyte in a form of solid particles.
 17. Theelectroerosion machining method of claim 13, wherein the removal agentcomprises a plurality of abrasive elements disposed on the respectiveone or more electrodes, and wherein the abrasive elements disposed onthe same one electrode are disposed alternately around and protrudebeyond the one electrode.
 18. The electroerosion machining method ofclaim 1, wherein the one or more electrodes are held via a base, andwherein more than one of the one or more electrodes are disposed on thebase alternately.
 19. The electroerosion machining method of claim 18,wherein the base defines a plurality of slots to hold the respectivemore than one electrode, a central hole in fluid communication with theelectrolyte supply and a plurality of channels in fluid communicationwith the central hole and the respective slots.
 20. The electroerosionmachining method of claim 13, wherein the one or more electrodescomprise wheel shapes.